As the level of integration of the LSI is increased, the circuit line widths of semiconductor devices are further made finer. As a method of forming a mask (a counterpart used by a stepper or a scanner is also called a reticle) for exposure for forming a circuit pattern in these semiconductor devices, an electron beam drawing technique having an excellent resolution performance is being used.
LER (Line Edge Roughness) of a pattern formed on a mask depends on the area density of the pattern and an irradiation amount of electron beam, and it is known that when the area density is high and the irradiation amount is low, the LER deteriorates. In mask drawing, in order to correct dimensional variation caused by a proximity effect which occurs at the time of drawing or by a loading effect which occurs in an etching process after the drawing, the irradiation amount for an area with a high pattern area density is often reduced, and the LER tends to deteriorate in such an area.
In order to improve the LER, an approach may be taken in which the irradiation amount is overall enhanced, that is, the base dose (the dose amount when the pattern density is 100%) is increased. However, when the base dose is increased, there is a problem in that dimensional displacement or positional displacement of a pattern occurs, or the throughput is decreased due to increase in an irradiation time.